first physics with the atlas detector
DESCRIPTION
First physics with the ATLAS detector. Dirk Zerwas LAL Orsay On behalf of the ATLAS Collaboration Physics at LHC 2008 Split, Croatia October 2, 2008. Introduction expected performance first physics conclusions. Introduction. Status of the ATLAS detector Peter Jenni - PowerPoint PPT PresentationTRANSCRIPT
First physics with the ATLAS detector
• Introduction• expected performance • first physics• conclusions
Dirk ZerwasLAL Orsay
On behalf of the ATLAS Collaboration
Physics at LHC 2008Split, Croatia
October 2, 2008
Introduction
• Status of the ATLAS detector Peter Jenni• Commissioning of the ATLAS detector Manuella Vincter
First physics = performance and calibrationHighlight expected performance: • electrons, muons, jet/ETmiss, tau, b-tagging, trigger• low-mass resonances, Z ee,μμ,ττ Z+jets, tt
First physics beyond performance: • new physics in autocalibrated/large cross section signals
Basis of the studies: CSC• large scale production • simulation and reconstruction of more than 25 million events• single particles to complex physics signatures• most precise detector description• volontary introduction of imperfections (alignment+additional material)• test of analysis model
EW: Z/W cross sections Lucia di Ciaccio (LHC) Kristin Lohwasser (ATLAS)QCD/top: Frank-Peter Schilling
Expected performance: Electronstalk by Emmanuel Turlay, September 30
Zee long range const term 100pb-1 :0.4% ( 0.5%) OK
Large QCD cross section at LHC:105 rejection reached for 64% efficiency: ok
Efficiency Zee tag& probe:Good agreement with MCtruth (±0.1%, ±1.5%)
First physics for electrons:• copious source of low-PT electrons: J/ψ/Upsilon• 100pb-1: Zee for intercalibration and tag&probe
Expected performance: Muons
Combination of ID and MuonSpectrometer tracks• Good efficiency PT>=4GeV with low fake rate• Good coverage in ηFirst physics: • Zμμ tag&probe• 100pb-1 ε ±0.08% (stat) ±1% (syst)• energy scale with 50pb-1: ±0.5GeV (50GeV muons)• initial misalignment 1mm and 1 mrad, no bias but 3x broader distribution (after aligment: 50μm)
Fake Rate
Expected performance: jets
talk by Damir Lelas September 30
Calorimeter based jets:• Topological clustering • Calibration (local) • Jet finding kt/cone• Jes corrections (noise/pileup)• Refined jets (underlying event)Jet energy scale ~ % in the barrel
Photon + jets: large statistics ~% scale precision Zee+1jet: 200pb-1 clear signal
Z+jet calibration
Expected performance: ETmiss
ETmiss at EM energy scale ~30%refined with • muons• electrons • jetsETmiss scale ~ 5%ETmiss resolution 0.57E
First check: Zττ energy scale 2%
Z W tt A A
Expected performance: Taus
calorimeter based tau-ID
Two approaches:• calorimeter based• track based• efficiencies: 30% for jet-rejection ~103
First physics:• 100pb-1
• W τν• Zττl+had• clear signal for W and Z in tau channel!
W τν
Zττl+had
ETmiss > 60GeV
Prel.
ATLAS Prel.
Expected performance: b-tagging
in-situ calibration of b-tagging: • tt: good agreement MCtruth and “MCData”• 5-10% precision• muon+jets with trigger prescaled • 50 pb-1 necessary, valid <80GeV
b-tagging: • 60% efficiency• JetProb: rejection at least 30• soft-lepton tagging (later)• IP3D (long. & transverse IP): rejection 60• secondary vertex: rejection 150
Expected performance: Trigger
electron trigger
jet trigger L1100pb-1
• sharp turn-on curves• differential cross section for jets
Total rates in budget !
Subset of Trigger Menu for 1031 cm-2s-1
prescale
Standard model: top quark
The LHC top quark factorysemi-leptonic top quark eventsno b-tagging used
First physics:• 100 pb-1 clear signal even with QCD bg x2• signal purity for the muon/electron channel 80%
100 pb-1: 508 signal events (muon channel)
electron channel
/ = 7% (stat) ± 15% (syst) ± 3% (pdf) ± 5%(lumi)
New physics: exotics
Electron channel alone: 100 pb-1 sensitivity 1TeVW’: 10 pb-1 sensitivity 1TeVCombines ETmiss and e/μ
First discovery physics:• extra gauge bosons eg. Z’, W’• necessitates electron/muon ID• ETmiss (W’)• alignment (seen in Z already) 1mm• typical limits currently 500GeV-1TeV
Z’ : 100pb-1 ~1.2-1.5TeVW’: 100pb-1 ~2TeV
New physics: Supersymmetry
ATLAS preliminary
1fb-1
Large cross sections for gluinos and squarks:• multi-jet + large ETmiss (+leptons)• necessitates understanding of all components
Define effective mass:• sum of jet PT and ETmiss• require one lepton• less statistics, but cleaner
Sensitivity:• 10pb-1 ~400GeV sensitivity=TeVatron• 1 fb-1 ~ 1.5TeV (all jets)• 1 fb-1 ~ 1TeV (1lepton + jets)
/100
pb
-1
102
101
1
0.1
0.01
l+jets
Conclusions
• ATLAS is well prepared for first physics• electrons (photons)• muons • jet• ETmiss • tau• b-tagging
• eagerly awaiting next year at 10 TeV (or more) to find:• the standard model• exotics• supersymmetry• or ?